This invention relates to a method of building construction that prevents or reduces the amount of soil and basement enclosure-sourced gases, moisture and biological and physical agents entering basement and other living spaces in building structures.
It is well known that buildings tend to act as chimneys or "stacks" throughout most of the year by drawing in cooler outside air through enclosure openings positioned below the neutral pressure plane of the building, which is located at about building mid-height, while simultaneously exhausting the warmed inside air above the neutral pressure plane of the building. This buoyancy-induced stack effect acts on all but hot summer days. It has been discovered only recently, however, that harmful and unpleasant substances are drawn from the surrounding soil, through basement cracks and openings, into the living space as a rsult of this stack effect. These unwanted harmful and unpleasant substances in the soil can also be forced into the living space through the action of wind pressure.
In addition to these two soil pollutant entry mechanisms, liquids in the soil containing harmful and unpleasant substances may penetrate basement wall and slab materials through capillary action and hence diffuse into the living space.
Sump pump, floor drain and service openings provide a fourth mechanism for the introduction of these harmful and unpleasant substances.
One group of pollutants that enter basements and are of current concern is radioactive radon gas and its progeny. These radionuclides emit the alpha radiation which is postulated to cause about five percent of all lung cancers making it the second leading cause of lung cancer after tobacco smoke. These radionuclides are emitted by rock, soil, underground water, and building materials such as concrete. Some five million North American homes are estimated to contain radon levels above the United States Environmental Protection Agency action level of 0.02 WL for radon progeny.
Other pollutants arising in the soil as a result of its natural organic content and the presence of waste materials, lawn fertilizers and herbicides therein, include methane and other gases, and fungal propagules and gaseous emissions. These gases and biological agents are also brought into the living space by means of these four basement entry mechanisms, as described above.
In addition to transporting dissolved gases, bacteria and soil fungal propagules into the living space, the introduction of soil moisture into the basement can result in damage and the formation of mold in affected building materials, carpets and furnishings, as well as coincidently attracting spiders, silverfish, centipedes, and other such insects. Moreover, these molds produce objectionable odors and/or allergic reactions. In some cases they cause illnesses and possibly compromise the human immune system. In addition, the occurrence of insects generally results in the use of pesticides indoors which introduces other harmful substances into the living space. Correcting basement concrete wall cracking and leakage is possibly the most costly and frequent repair in new dwellings.
Various methods have been proposed to reduce or prevent the entry of soil pollutants. These have included plugging cracks in foundation slabs and basement walls, and sealing and venting sump pumps and other such openings. With such an ad hoc preventative approach, however, it is virtually impossible to permanently seal all cracks, and thus, the entry of soil pollutants or foundation water by this mechanism is never fully and permanently prevented. As well, as the air pressure of the basement area is generally at a lesser air pressure than that of the external soil air, soil gases are drawn into any openings into the building structure.
Other methods have also been proposed, but these are also problematic. These other methods include exhausting the weeping tile to the outdoor air so as to depressurize around the slabwall interface, and exhausting or pressurizing a gravel layer below the slab so that any soil gases may escape to the atmosphere without entering the basement. However, such approaches do not deal with finished basement water leakage and condensation problems. As well, weeping tile can become plugged and the layer of gravel may not allow free air movement to the exhaust. Further, since moisture and entrained gases can travel through the concrete by a combination of capillary action followed by near surface diffusion, this entry mechanism is not adequately dealt with by subslab ventilation. As well, basement foundation building materials such as concrete and biocide-treated wood can themselves be sources of basement living space air pollutants, and this source of pollutants is not adequately addressed by other methods.